It is well known to provide a roll up, or retractable, screen assembly that can extend across a window or door. In most cases, a flexible screen can be wound about a wooden, metal or plastic rod or pole which is positioned in a substantially horizontal manner such that the screen assembly can be pulled up or pulled down in a vertical direction. A holland blind is an example of this type of screen assembly.
It is also known to provide a retractable screen assembly that can move in a horizontal direction across a window or door cavity, and with this type of assembly, the screen (for instance a mesh) can be wound about a substantially vertical rod or pole (typically located at one side of the cavity).
The present invention is directed primarily to a screen assembly that can move horizontally across a window or door cavity. However, there may be parts of the invention which may find suitability in “up and down” screens or screens which are extended and retracted in other manners.
There is a general requirement that the flexible screen is placed under tension to keep it relatively taut when pulled from the retracted position to the extended position. For vertically moving (that is up and down moving) screen assemblies, this can be quite easily achieved by providing some type of weight on the bottom edge of the screen. However, for horizontally moving screen assemblies, this cannot be easily done. Also, it is not satisfactory to simply turn a vertically moving screen assembly on its side to make a horizontally moving screen assembly. For instance, one disadvantage is that gravity cannot be used to tension the screen material (as is the case with vertically moving screens). Another disadvantage is that the screen material has a tendency to sag as it is pulled across which is unsightly and can create gaps and openings and damage to the mechanism.
A known solution to provide tension with horizontally moving screen assemblies is to provide some form of spring to maintain tension in the screen material. The spring can be placed within a hollow tube about which the screen material is wound. Extension (unrolling) of the screen material from the tube causes the spring to be increasingly “wound up” to create tension (a “pullback” force) in the screen material.
A disadvantage with this arrangement is that the amount of tension increases as more of the screen material is unwound from the tube. This means that it can become progressively more difficult to pull the screen material further across the window or door cavity from one side to the other. It should be appreciated that one use of the screen assembly is across rather large door cavities that can have a length of between 3-6 m, and usually contain bifold doors or multi-sliding doors. Thus, it can become very difficult to pull a screen across the door cavity as the tension can become too large—especially with a single screen spanning 3 meters or more. If the tension is reduced to compensate, the screen material can sag due to insufficient tension, or have sag lines.
Another disadvantage with the above type of arrangement, is that once the screen has been pulled across, and latched or otherwise connected to the other side of the door or window cavity, if the screen is unlatched, it can retract very quickly to the other side of the door or window cavity which is quite unsuitable.
Another disadvantage with the above type of arrangement, is that the increasing tension can cause damage (for instance premature stretching) of the screen material, especially if the screen material is relatively flimsy. There is an advantage in having screen material which is relatively thin (and therefore may be somewhat flimsy), as it allows a greater length of material to be wound about the tube without making the diameter to large to be neatly hidden away in one side of the cavity.
An attempted solution to this problem has been to introduce some form of brake. However, any form of brake can increase the number of parts in the assembly, and require constant maintenance and possible replacement, can fail under wet conditions or if debris or grime come into contact with the brake, and therefore the concept of having some form of brake is generally undesirable
It is also known to try to balance the tension on the screen, in essence, to try to reduce the increasing tension force as the screen is pulled across the window or door cavity. Various arrangements of counterweights have been tried to provide some type of balance to the tension force. These counterweights may comprise a weighted rod attached to the end of a line member. Other arrangements use various types of “counter” spring arrangements to provide a balance.
A disadvantage with the use of counterweights is the problem with inertia. To explain, when the screen is in the extended position, and typically pulled across the window or door cavity and latched to the other side, if it is desired to open the screen by pulling the screen partially back away from the other side of the window and door cavity, doing so will cause acceleration or deceleration of the counterweights, and the consequence of this is that the screen will always feel “heavy” to operate quickly which is quite undesirable. Thus, the use of counterweights, and particularly the very large and heavy counterweights may not be a general solution to overcome the problem with all types of screens, but the present invention may be able to accommodate some form of counterweight.
A disadvantage with the use of a “counter” spring is that the spring can only produce a complete neutralisation or balance of the tension at only one extended position. Put differently, with the use of a counter spring, the screen can be pulled across and pulled back more easily than without a counter spring, but if the screen is let go, the “balance” position will be somewhere across the door or window cavity. While this arrangement has some advantages, there is still the general disadvantage that there will always be some resistance to movement of the screen across the window or door cavity except at the one particular “balance” point. It is generally not possible to vary the counter spring in a continuous manner such that the screen is always balanced no matter where the screen is across the door cavity.
It is also known to provide a screen that can be pulled across a door or window or other type of cavity and where there is also provided a line member and pulleys etc to assist in the extension and the retraction of the screen. For a horizontally extending screen, it is known to have a vertical rod, typically at one end of the cavity, and about which to screen material can be wound/unwound, and pulleys or similar devices at the other end of the cavity, with a line member (typically a steel wire, plastic wire etc) connecting the various parts.
It is also known to provide a horizontally extending screen where the screen material wraps around a vertical support member, and where the vertical support member is hollow, and a spring is provided in the vertical support member. A disadvantage with this arrangement is that if the spring requires adjustment, is quite difficult to access the spring to do so.
Therefore, there would be an advantage if it were possible to have a screen assembly containing some form of biasing means or spring and where the spring is not situated within the supporting member.
There is an advantage in being able to provide a mechanism that can substantially balance the tension force of the screen at any position across the door window cavity such that, if the screen is let go at any position, the screen will simply remain still and will not retract or further extend, and where the mechanism is reliable in operation.
There is also an advantage is being able to provide a mechanism generally as described above and which is relatively simple in manufacture and design.
Referring again to the screens that have a single “balance” point, there is sometimes an advantage in providing a screen assembly, and typically a “pull across” screen assembly which is relatively easy to manipulate and which has at least one balance point, and which, when positioned somewhat away from the balance point, will naturally move back to the retracted position or naturally move forward to the extended position. Thus, there may be an advantage in having a screen assembly which is not balanced at each and every point of extension but which is balanced at some point, and “partially” balanced at other points by which is meant that at these other points, the screen will slowly either retract or extend. An advantage of this assembly (and in contrast to some existing assemblies) is that there is little likelihood of the screen retracting or extending very quickly, because the screen is partially balanced.
There would also be an advantage if it were possible to provide a screen assembly which can also have some form of adjustment means to compensate for irregularities in the shape of the door cavity.
Many known types of pull across (horizontally extending) or up-and-down (vertically extending) have some sort of mechanism to balance the screen. It is known to use a tapered drum or frusto conical pulley to “tune” the drum to the width of the roll of screen material on the rod. U.S. Pat. No. 262,398 [1882] describes such an arrangement.
To provide smooth operation of the screen, a drum/pulley is placed on each end of the horizontal rod (for an up-and-down) motion or on the upper and lower end of a vertical rod (for a pull across screen). US 2005/0051283, EP911476, FR 2594173, JP9303068, FR2558518, DE3936913, and CA 2027827 describe such dual drum/pulley arrangements.
A disadvantage with these dual drum arrangements, is that they are generally not suitable for use with a vertical rod in a pull across screen, as the lower drum must be recessed into the floor/ground which is not desirable, as the drum is prone to damage, may be a tripping hazard, looks unsightly, and can accumulate dirt and debris which can effect the proper operation of the drum.
FR 2563860 describes a pull across screen comprising only an upper drum, but to ensure smooth operation, a motor is used to operate the screen.
Therefore, there would be an advantage to provide a pull across screen which does not require a lower drum and which can be extended or retracted in a balanced manner and which has a particular line and spring arrangement to enable this to occur. The screen can be operated manually, and it is not essential to have a motor (although a motor can be used if desired).
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.